Soft-Core Processors For Embedded Systems - Research Centre for ...

RESEARCH CENTRE FOR INTEGRATED MICROSYSTEMS - UNIVERSITY OF WINDSOR

Soft-Core Processors For Embedded Systems Jason G. Tong and Ian D. L. Anderson Supervisor: Dr. M.A.S. Khalid ICM’06, December 2006 Research Center for Integrated Microsystems Department of Electrical and Computer Engineering University of Windsor

18th International Conference on Microelectronics – December 16th – 19th, 2006

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OUTLINE • Introduction • A Survey of Soft-Core Processors • Commerical Cores and Tools • Open-source Cores • Some Example Applications • Comparison of Soft-Core Processors • Conclusions and Future Work


Slide 2


Introduction


Slide 3


Embedded Systems • An embedded system: a system that utilizes custom hardware and software to carry out specific tasks • Digital Hardware: – Microprocessor or µC – Application-specific hardware generally used for accelerating timecritical tasks • Embedded software running on the μP or μC

Embedded System Embedded CPU Software running on CPU

Memory & I/O Applicationspecific hardware


Slide 4


Core-Based Design • It makes sense for many designers to reuse pre-designed hardware components called “Intellectual Property (IP) Cores” • Reduce design time at the expense of area/performance penalty • Soft-core processors – Complete microprocessors described in a hardware description language (HDL) such as VHDL, Verilog, etc. 18th International Conference on Microelectronics – December 16th – 19th, 2006

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Advantages of Soft-Core Processors • Higher level of abstraction – easier to understand • More flexible – designers can change the core by editing source code or selecting parameters (more on that later) • Platform independent – can be synthesized for any IC technology, including FPGAs, ASICs, etc. – More immune to obsolescence


Slide 6


A Survey of Soft-Core Processors


Slide 7


Commercial Cores and Tools • Some of the well known commerical cores are: • Altera’s Nios II • Xilinx’s MicroBlaze and PicoBlaze • Tensilica’s Xtensa


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Nios II Processor • Nios II – The second generation of 32-bit Reduced Instruction Set Computer (RISC) Processor by Altera • A configurable processor that can be used in many embedded system applications (e.g., Printers, Medical Instrumentation, DVD Players, etc.) • Targeted for multiple Altera FPGAs (e.g., Cyclone Series FPGAs, Stratix Series FPGAs) • Instantiated using Altera’s System On Programmable Chip (SOPC) CAD Tool


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Nios II Processor •

Nios II Processor (A 32-bit RISC Soft-Core Processor) • 32 General Purpose Registers • 32 Interrupt Request Registers • Separate Instruction and Data Cache (up to 64KBytes) • Single Instruction 32x32 Multiplier and Divider • Dedicated 64-bit and 128-bit multiply instructions • Tightly Coupled Memory (TCM) Modules • Three variant cores: Economy, Standard, Fast


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Nios II Processor Economy Core – Optimized for Area, but provides sufficient performance for small applications (e.g., TV Remote Control, Digital Clock)

Standard Core – Trade off between Economy and Fast cores. Better performance than Economy can offer. But consumes more LEs (e.g., Microwave Oven Controller, DVD Players) Fast Core – Optimized for best performance on computationally intensive applications. But consumes the most LEs (e.g., multimedia applications) Courtesy of Paramount and Universal Studios, USA California


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Nios II Processor Comparison Nios II Variants Features

Nios II Economy

Nios II Standard

Nios II Fast

Objective

Optimized for size

Balance between size and Speed

Optimized for High Performance

Caches (Instruction/Data)

None

Up to 64KB / None

64KB / 64KB

Pipeline Stages

1

5

6

Hardware Multiply

Software Emulated

3 Cycles per MUL

1 Cycle per MUL

Logic Elements used

600-700

1200-1400

1400-1800

Custom Instructions

256 Custom Instructions


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Xilinx MicroBlaze •

•

•

MicroBlaze – a 32-bit soft-core processor optimized for embedded applications Features: • Harvard RISC architecture • 32-bit instructions • 3-stage pipeline • 32 general-purpose registers Image Source: MicroBlaze Product Brief http://www.xilinx.com/bvdocs/ipcenter/product_brief/MB_sell_sheet.pdf • Shift unit • 2 levels of interrupt Has a number of options including FPU, hardware divider, barrel shifter, caches, etc – save area by not using these options if not needed


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Xilinx MicroBlaze •

• •

Can be connected to on-chip and off-chip peripheral components such using the general-purpose On-chip Peripheral Bus (OPB) Interfaced to memory via the Local Memory Bus (LMB) or the OPB Designers can use the Fast Simplex Link (FSL) to interface custom hardware accelerators directly to the pipeline • FSL - a low-latency interface to the MicroBlaze pipeline

Image Source: MicroBlaze Product Brief http://www.xilinx.com/bvdocs/ipcenter/product_brief/MB_sell_sheet.pdf


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Xilinx PicoBlaze • • •

A small 8-bit soft-core microcontroller for simple processing applications Specifically optimized for the Virtex and Spartan families of FPGAs, and the CoolRunner-II CPLDs VHDL source-code can be downloaded for free from Xilinx Inc.’s website


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Tensilica Xtensa • •

•

Tensilica’s flagship product: the Xtensa Series of “configurable and extensible” processors Configurable: base core features a set of parameters: • Hardware multipliers, single precision IEEE-754 compatible FPU, varying number of interrupts, cache sizes and write policies, variable instruction and data memory sizes, and others Extensible: designers invent custom instructions using the Tensilica Instruction Extension (TIE) language – a Verilog-like language • The TIE instructions are turned into hardware using the TIE compiler


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Xtensa Design Environment •

•

•

The Xtensa Xplorer – a complete design environment for Xtensa processors The XPRES Compiler can analyze a C/C++ algorithm and automatically create TIE extensions The Xtensa Processor Generator generates HDL code and Electronic Design Automation (EDA) scripts for a customized processor Image Source: Xtensa Developer’s Toolkit Product Brief http://www.tensilica.com/pdf/xtensa_processor_v3.pdf


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Open-Source Cores • There are numerous soft-cores freely available from open-source communities across the internet • Two will be reviewed: • LEON by Gaisler Research • OpenRISC 1200 from opencores.org


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LEON by Gaisler Research • The LEON line of synthesizable processors: based on the SPARC Version 8 architecture • LEON2 and LEON3: open-source VHDL models Image Source: LEON2 Processor Overview of 32-bit processing cores http://www.gaisler.com/cms4_5_3/index.php?option=com_content&task=vi ew&id=12&Itemid=52 • Integer unit fully compliant with IEEE-1754 SPARC V8 standard • Hardware multiply, divide and multiply-accumulate (MAC) units • LEON2 – 5-stage pipeline, LEON3 – 7-stage pipeline • Several peripherals available, including FPUs, timers, UARTs, interrupt controllers, etc. 18th International Conference on Microelectronics – December 16th – 19th, 2006

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OpenRISC 1200

Image Source: OpenRisc 1200 http://www.opencores.org/projects.cgi/web/or1k/openrisc_1200

• • •

One of the popular processors at www.opencores.org Contains either a 32/64-bit RISC Architecture and a 5-stage pipelined processor Harvard architecture, containing separate 8KB data and instruction memories


Slide 20


OpenRISC 1200


• • • •

High performance CPU/DSP architecture – 32-bit architecture implementing ORBIS32 instruction set Advanced Debug Module – non-intrusive debug module for debugging of the OpenRisc processor Tick Timer – System Clock Timer Instruction/Data Memory Management Unit – Harvard Style memory organization, 8KB of instruction/data cache memories


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OpenRISC 1200


• • • • •

Synthesizable and downloadable onto Altera or Xilinx FPGAs Real-Time Operating System (RTOS) Support: Linux, Micro-Linux, and OAR RTEMS Programming Languages Support: C/C++/Java/Fortran Peak Performance: 250MHz and 250DMIPS Additional Features: Floating Point Unit and up to 8 peripherals can be connected to the processor core


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Some Example Applications


Slide 23


Communications - Broadcom • Broadcom used the Xtensa Processor in the BCM1500 Project • Designed a class of access communication components for voice, video and data networking • Five Xtensa Processors were used in their CALISTOTM architecture which manages computationally intensive communications functions: • e.g. echo cancellation

Image Source: CALISTO VoP Product Brief http://www.broadcom.com/collateral/pb/1500VoP-PB03-R.pdf


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Communications – Cisco Systems • Cisco Systems’ Carrier Routing System (CRS-1) • Uses 192 Xtensa Processors in the Cisco Silicon Packet Processor • CRS-1 is the only carrier routing system capable of scaling up to 92 terabits per second

Image Source: Cisco Carrier Routing System http://www.cisco.com/application/pdf/en/us/guest/products/ps5 763/c1031/cdccont_0900aecd800f8118.pdf


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Advertising - AED •

•

• •

Advanced Electronic Designs (AED) created an LED sign for JPMorgan ChaseTM in Times Square in New York City 135 feet long and 26 feet high with a resolution of nearly Image Source: Sign of the Times Xilinx Xcell Journal, Winter 2004 2 million pixels Used Virtex and Spartan FPGAs and over 1,000 PicoBlaze processors One main use of processors: Ethernet controllers used to send data to different parts of the sign


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Security and Authentication - UCLA •

•

•

A team of researchers a UCLA have developed the ThumbPod – an FPGA based fingerprint authentication device The LEON2 processor is used along with two co-processors: • Advanced Encryption Standard (AES) processor • Discrete Fourier Transform (DFT) processor The ThumbPod is able to capture a fingerprint, extract its features and return a score from 0 to 100 indicating the degree of matching

Image Source: ThumbPod Puts Security Under Your Thumb Xilinx Xcell Journal, Winter 2004


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Comparison of Soft-Core Processors


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Comparison of Soft-Cores Nios II (Fast Core)

MicroBlaze

Xtensa XL

OpenRISC 1200

LEON3

Speed MHz (ASIC/FPGA)

200 MHz (FPGA)

200 MHz (FPGA)

350MHz (ASIC)

300MHz (ASIC)

125MHz/400MHz (FPGA/ASIC)

FPGA/ASIC Tech.

Stratix/ Stratix II

Virtex-4

0.13 micron

0.18 micron

0.13 micron

Reported DMIPS

150 DMIPs

166 DMIPs

N/A

300DMIPS

85DMIPs

32-bit RISC

32-Bit RISC

32-bit RISC

32 or 64-bit RISC

32-bit RISC

Up to 64KB

Up to 64KB

Up to 32KB (1)

Up to 64KB

Up to 256KB

Floating Point Unit (optional)

IEEE 754

IEEE 754

IEEE 754

as peripheral

IEEE 754

Pipeline

6 Stages

3 Stages

5 Stages

5 Stages

7 Stages

Custom Instructions

Up to 256 Instructions

None

Unlimited

Unspecified limit

None

Register File Size

32

32

32 or 64

32

2-32

Implementation

FPGA

FPGA

FPGA, ASIC

FPGA, ASIC

FPGA/ASIC

Area

700-1800 LEs

1269 LUTs

0.26mm^2

N/A

N/A

ISA Cache Memory (I/D)

(1) – Using 1,2 or 4-way set associative configuration


Slide 29


Comparison of Soft-Cores •

Leon3 has the highest operating frequency of 400MHz using ASIC Implementation

•

Nios II and Microblaze, both have the highest operating frequency at 200 MHz on FPGA Implementation

•

Tensilica Xtensa offers the greatest flexibility since designers have the ability to implement unlimited custom instructions and execution units in the processor’s core

•

Majority of the soft-core processors have an optional FPU which is added as a component in the processor’s core or as a peripheral


Slide 30


Conclusion and Future Work •

Soft-core processors are becoming an attractive alternative for embedded system design due to the flexibility they offer • More wide-spread usage for embedded system design

Related research at RCIM •

• •

A CAD tool is currently under development which enables designers to build soft-core processors and explore various architecture trade-offs (Ian Anderson & Omar Alryahi) • Next few slides introduce this CAD tool Aws Ismail exploring NoC implementation on FPGAs Jason Tong developed an accurate, non-intrusive, FPGA-based SW profiling tool for NIOS II based embedded systems


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SCBuild: A CAD Tool for the DSE of Parameterized Cores

18thAnderson International Conference on Microelectronics M.A.Sc – December 16th – 19th, 2006 Defense Ian

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Purpose of SCBuild • “SC” stands for “Soft-core” • A software tool that performs the following tasks: • Facilitates rapid exploration of the design space of a parameterized core using the SEAMO algorithm • Generates variants of a soft-core based on a user-selected set of parameter values • In other words, the user specifies the parameter values and SCBuild generates a VHDL description of it automatically


Slide 33 33


SCBuild System Environment • Template Architect: generates a Template Description for a given hardware component • SCBuild takes this description and instantiates VHDL components from the Library to create a softcore • Also performs DSE using SEAMO algorithm

(Not part of this present research)

Template Architect Tool Template Description

SCBuild

Template Component Library

User inputs parameter selection

VHDL Component Library

VHDL Description of Core


Slide 34 34


CAD Flow for SCBuild Design Entry Check XML Syntax

Correct?

No

Yes

Collect System-level Parameters DSE and Parameter Selection Elaboration Create and Compile Quartus II Project (Optional)


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References • • • • • • •

[6] Xilinx Incorporated Website, www.xilinx.com, June 2006 [7] “MicroBlaze Processor Reference Guide”, Xilinx Corporation, October 5, 2005 [8] “PicoBlaze 8-bit Embedded Microcontroller User Guide”, Xilinx Corporation, November 21, 2005 [9] Tensilica Incorporated Website, www.tensilica.com, June 2006 [10] “Tensilica Diamond Standard Series Product Brief”, Tensilica Incorporated, 2006 [11] Tom R. Halfhill, “Tensilica’s Preconfigured Cores”, Microprocessor Report, March 20, 2006 [12] Xtensa Overview, www.tensilica.com/products/overview.htm, June 2006


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References • • • • • • • •

[13] Create TIE, www.tensilica.com/products/create tie.htm, Septembe 2006 [14] TIE Compiler, www.tensilica.com/products/tie compiler.htm, September 2006 [15] XPRES Compiler, http://www.tensilica.com/products/xpres.htm, September 2006 [16] Opencores.org Website, www.opencores.org, June 2006 [17] UT Nios Homepage, www.eecg.toronto.edu/˜plavec/utnios.html, June 2006 [18] OpenSPARC Website, www.opensparc.org, June 2006 [19] Gaisler Research Website, www.gaisler.com, June 2006 [20] “LEON2 Processor User’s Manual XST Edition”, Gaisler Research, July 2005


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References • • • • • •

•

[21] “GRLIB IP Core User’s Manual”, Gaisler Research, February 2006 [22] Broadcom Website, www.broadcom.com, June 2006 [23] “Broadcom CALISTOTM BCM1500 Leverages Multiple Xtensa Cores for VoIP ASSP”, Tensilica Incorporated Success Story, 2001 [24] “Tensilica Technology Helps Power World’s Fasted Router”, Tensilica Incorporated Press Release, August 2, 2004 [25] Advanced Electronics Designs Incorporated Homepage, http://www.advanced.pro/, September 2006 [26] Daughenbaugh, J., “Sign of the Times, Xilinx makes high-tech outdoor advertising in Times Square possible”, Xilinx Xcell Journal, Winter 2004 [27] Schaumont, P. and Verbauwhede, I., “ThumbPod puts security under your thumb”, Xilinx Xcell Journal, Winter 2004


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